1. Field of the Invention
The present invention relates to a structure for mounting an LSI package onto a photoelectric wiring board, and its mounting method. In particular, the present invention relates to a mounting structure for mounting an optical interface having an optical element and an LSI package having an LSI chip mounted thereon onto a photoelectric wiring board, and its mounting method.
2. Related Art
For the transmission of signals between LSIs or between an LSI and a backplane in information devices such as routers and servers, the optical signal transmission system that is fast in speed and low in crosstalk and noise is being adopted. When forming an optical signal transmission system in this case, the method for mounting the optical interface to conduct photoelectric conversion (or electro-optic conversion) poses a problem. For mounting an LSI package having an optical interface onto the surface of a photoelectric wiring board having an optical transmission line and electric wiring laid down on a substrate, optically connecting the photoelectric wiring board to the optical interface with a sufficient precision, and raising the practicality, first, it is necessary that optical axis alignment between a plurality of optical elements mounted on the optical interface and the optical transmission line can be achieved with a sufficient precision. For example, in the case where the optical transmission line is a multi-mode optical waveguide having a core section shape of 40 μm square, the allowable optical axis misalignment quantity is 20 μm or less. Secondly, it is necessary that positioning and fixing can be conducted with high work efficiency and high precision without conducting complicated optical axis adjustment work, considering the mass production efficiency of products. Thirdly, from the viewpoint of the apparatus maintenance and easiness of modification, it is necessary that only an LSI package can be replaced easily without melting solder or using a chip bonder when replacing the LSI package.
As for a structure for mounting an LSI package having an optical interface onto a photoelectric wiring board, a technique using solder bumps for the mounting is known (see, for example, JP-A-2000-332301). FIG. 1A is an oblique view of a conventional example described in JP-A-2000-332301. FIG. 1B is its partial section view taken along a 1B-1B line. In this conventional example, an optical element array 12 is mounted directly on an LSI chip 11 by using solder bumps 13 as shown in FIGS. 1A and 1B. The LSI chip 11 is mounted on a print-circuit board 17 having an optical waveguide 16 mounted thereon, by using metal posts 14 and solder bumps 15. In this structure, optical axis alignment between an optical element and the waveguide is automatically achieved without adjustment owing to a self-alignment effect obtained at the time of solder bump fusion. Therefore, it is possible to satisfy the above-described first and second requirements.
Furthermore, a technique for positioning an optical fiber on an optical element by using an optical fiber connector and a receptacle is also known (see, for example, JP-A-5-251717). FIG. 2 is a sectional view of a conventional example described in JP-A-5-251717. In this conventional example, a semiconductor chip 21 having a wiring layer 21a and having an optical element 22 embedded within a substrate is mounted on a base 24 having a receptacle 25 mounted thereon and having input & output pins planted thereon. Furthermore, other semiconductor chips 23 are mounted on the wiring layer 21a of the semiconductor chip 21. An optical fiber connector 27 is connected to an optical fiber cable 26. The optical fiber cable 26 is optically coupled to the optical element 22 by fitting connector pins 25a of a receptacle 25 into guide holes 27a of the optical fiber connector 27.